Synthesis and Properties of the Helium Clathrate and Defect Perovskite [He □ ][CaNb]F.

The defect double perovskite [He □ ][CaNb]F, with helium on its A-site, can be prepared by the insertion of helium into ReO-type CaNbF at high pressure. Upon cooling from 300 to 100 K under 0.4 GPa helium, ∼60% of the A-sites become occupied.

Pressure-Induced Dislocations and Their Influence on Ionic Transport in Li-Conducting Argyrodites.

The influence of the microstructure on the ionic conductivity and cell performance is a topic of broad scientific interest in solid-state batteries. The current understanding is that interfacial decomposition reactions during cycling induce local strain at the interfaces between solid electrolytes and the anode/cathode, as well as within the electrode composites. Characterizing the effects of internal strain on ion transport is particularly important, given the significant local chemomechanical effects caused by volumetric changes of the active materials during cycling.

Neutron scattering study of polyamorphic THF·17(HO) - toward a generalized picture of amorphous states and structures derived from clathrate hydrates.

From crystalline tetrahydrofuran clathrate hydrate, THF-CH (THF·17HO, cubic structure II), three distinct polyamorphs can be derived. First, THF-CH undergoes pressure-induced amorphization when pressurized to 1.3 GPa in the temperature range 77-140 K to a form which, in analogy to pure ice, may be called high-density amorphous (HDA).

Structural investigation of three distinct amorphous forms of Ar hydrate.

Three amorphous forms of Ar hydrate were produced using the crystalline clathrate hydrate Ar·6.5HO (structure II, 3̄, ≈ 17.1 Å) as a precursor and structurally characterized by a combination of isotope substitution (Ar) neutron diffraction and molecular dynamics (MD) simulations.

3D-printed BC collimation for neutron pressure cells.

A design for an incident-beam collimator for the Paris-Edinburgh pressure cell is described here. This design can be fabricated from reaction-bonded BC but also through fast turnaround, inexpensive 3D-printing. 3D-printing thereby also offers the opportunity of composite collimators whereby the tip closest to the sample can exhibit even better neutronic characteristics.

Decoupling Lattice and Magnetic Instabilities in Frustrated CuMnO.

The AMnO delafossites (A = Na, Cu) are model frustrated antiferromagnets, with triangular layers of Mn spins. At low temperatures ( = 65 K), a 2/ → 1̅ transition is found in CuMnO, which breaks frustration and establishes magnetic order. In contrast to this clean transition, A = Na only shows short-range distortions at .

Distance-Selected Topochemical Dehydro-Diels-Alder Reaction of 1,4-Diphenylbutadiyne toward Crystalline Graphitic Nanoribbons.

Solid-state topochemical polymerization (SSTP) is a promising method to construct functional crystalline polymeric materials, but in contrast to various reactions that happen in solution, only very limited types of SSTP reactions are reported. Diels-Alder (DA) and dehydro-DA (DDA) reactions are textbook reactions for preparing six-membered rings in solution but are scarcely seen in solid-state synthesis. Here, using multiple cutting-edge techniques, we demonstrate that the solid 1,4-diphenylbutadiyne (DPB) undergoes a DDA reaction under 10-20 GPa with the phenyl as the dienophile.

Exploiting Symmetry Mismatch to Control Magnetism in a Ferroelastic Heterostructure.

In the bulk, LaCoO_{3} (LCO) is a paramagnet, yet the low-temperature ferromagnetism (FM) is observed in tensile strained thin films, and its origin remains unresolved. Here, we quantitatively measured the distribution of atomic density and magnetization in LCO films by polarized neutron reflectometry (PNR) and found that the LCO layers near the heterointerfaces exhibit a reduced magnetization but an enhanced atomic density, whereas the film's interior (i.e.

Absence of amorphous forms when ice is compressed at low temperature.

Amorphous water ice comes in at least three distinct structural forms, all lacking long-range crystalline order. High-density amorphous ice (HDA) was first produced by compressing ice I to 11 kilobar at temperatures below 130 kelvin, and the process was described as thermodynamic melting, implying that HDA is a glassy state of water. This concept, and the ability to transform HDA reversibly into low-density amorphous ice, inspired the two-liquid water model, which relates the amorphous phases to two liquid waters in the deeply supercooled regime (below 228 kelvin) to explain many of the anomalies of water (such as density and heat capacity anomalies).

Giant Barocaloric Effect at the Spin Crossover Transition of a Molecular Crystal.

The first experimental evidence for a giant, conventional barocaloric effect (BCE) associated with a pressure-driven spin crossover transition near room temperature is provided. Magnetometry, neutron scattering, and calorimetry are used to explore the pressure dependence of the SCO phase transition in polycrystalline samples of protonated and partially deuterated [FeL ][BF ] [L = 2,6-di(pyrazol-1-yl)pyridine] at applied pressures of up to 120 MPa (1200 bar). The data indicate that, for a pressure change of only 0-300 bar (0-30 MPa), an adiabatic temperature change of 3 K is observed at 262 K or 257 K in the protonated and deuterated materials, respectively.

Tunable multiferroic order parameters in Sr- Ba Mn- Ti O.

Responding to the rapidly increasing demand for efficient energy usage and increased speed and functionality of electronic and spintronic devices, multiferroic oxides have recently emerged as key materials capable of tackling this multifaceted challenge. In this paper, we describe the development of single-site manganese-based multiferroic perovskite materials with modest amounts of nonmagnetic Ti substituted at the magnetic Mn site in Sr- Ba Mn- Ti O (SBMTO). Significantly enhanced properties were achieved with ferroelectric-type structural transition temperatures boosted to ∼430K.

Direct observation of symmetrization of hydrogen bond in δ-AlOOH under mantle conditions using neutron diffraction.

At ambient pressure, the hydrogen bond in materials such as ice, hydrates, and hydrous minerals that compose the Earth and icy planets generally takes an asymmetric O-H···O configuration. Pressure significantly affects this configuration, and it is predicted to become symmetric, such that the hydrogen is centered between the two oxygen atoms at high pressure. Changes of physical properties of minerals relevant to this symmetrization have been found; however, the atomic configuration around this symmetrization has remained elusive so far.

A suite-level review of the neutron powder diffraction instruments at Oak Ridge National Laboratory.

The suite of neutron powder diffractometers at Oak Ridge National Laboratory (ORNL) utilizes the distinct characteristics of the Spallation Neutron Source and High Flux Isotope Reactor to enable the measurements of powder samples over an unparalleled regime at a single laboratory. Full refinements over large Q ranges, total scattering methods, fast measurements under changing conditions, and a wide array of sample environments are available. This article provides a brief overview of each powder instrument at ORNL and details the complementarity across the suite.

The high pressure gas capabilities at Oak Ridge National Laboratory's neutron facilities.

The study of samples subjected to high pressure gas is an important asset in materials research and has consequently been a priority of the sample environment development at the Oak Ridge National Laboratory's (ORNL) neutron program. Such effort has resulted in the availability of an extensive combination of pressure cells and gas intensifiers (both commercially available and custom made). These resources are available across both neutron facilities at ORNL: the Spallation Neutron Source and the High Flux Isotope Reactor.

Next-generation diamond cell and applications to single-crystal neutron diffraction.

A diamond cell optimized for single-crystal neutron diffraction is described. It is adapted for work at several of the single-crystal diffractometers of the Spallation Neutron Source and the High Flux Isotope Reactor at the Oak Ridge National Laboratory (ORNL). A simple spring design improves portability across the facilities and affords load maintenance from offline pressurization and during temperature cycling.

Compression mechanisms of ferroelectric PbTiO via high pressure neutron scattering.

Switchable atomic displacements generate electric dipole moments in ferroelectric materials utilized in many contemporary devices. Lead titanate, a perovskite oxide with formula PbTiO, has been referred to as a textbook example of a prototype displacive ferroelectric and is a testing platform of widely used models of piezoelectric response of complex solid-solutions. PbTiO has been addressed by experimental and computational studies, often with apparently conflicting conclusions.

Mechanochemical Synthesis of Carbon Nanothread Single Crystals.

Synthesis of well-ordered reduced dimensional carbon solids with extended bonding remains a challenge. For example, few single-crystal organic monomers react under topochemical control to produce single-crystal extended solids. We report a mechanochemical synthesis in which slow compression at room temperature under uniaxial stress can convert polycrystalline or single-crystal benzene monomer into single-crystalline packings of carbon nanothreads, a one-dimensional sp carbon nanomaterial.

Synthesis of Defect Perovskites (He□)(CaZr)F by Inserting Helium into the Negative Thermal Expansion Material CaZrF.

Defect perovskites (He□)(CaZr)F can be prepared by inserting helium into CaZrF at high pressure. They can be recovered to ambient pressure at low temperature. There are no prior examples of perovskites with noble gases on the A-sites.

Novel diamond cells for neutron diffraction using multi-carat CVD anvils.

Traditionally, neutron diffraction at high pressure has been severely limited in pressure because low neutron flux required large sample volumes and therefore large volume presses. At the high-flux Spallation Neutron Source at the Oak Ridge National Laboratory, we have developed new, large-volume diamond anvil cells for neutron diffraction. The main features of these cells are multi-carat, single crystal chemical vapor deposition diamonds, very large diffraction apertures, and gas membranes to accommodate pressure stability, especially upon cooling.

Pressure induced polymerization of acetylide anions in CaC and 10 fold enhancement of electrical conductivity.

Transformation between different types of carbon-carbon bonding in carbides often results in a dramatic change of physical and chemical properties. Under external pressure, unsaturated carbon atoms form new covalent bonds regardless of the electrostatic repulsion. It was predicted that calcium acetylide (also known as calcium carbide, CaC) polymerizes to form calcium polyacetylide, calcium polyacenide and calcium graphenide under high pressure.

Pressure-Induced Polymerization of Acetylene: Structure-Directed Stereoselectivity and a Possible Route to Graphane.

Geometric isomerism in polyacetylene is a basic concept in chemistry textbooks. Polymerization to cis-isomer is kinetically preferred at low temperature, not only in the classic catalytic reaction in solution but also, unexpectedly, in the crystalline phase when it is driven by external pressure without a catalyst. Until now, no perfect reaction route has been proposed for this pressure-induced polymerization.

Deuterium Isotope Effects in Polymerization of Benzene under Pressure.

The enormous versatility in the properties of carbon materials depends on the content of the sp and sp covalent bonds. Under compression, if intermolecular distances cross a critical threshold, then unsaturated hydrocarbons gradually transform to saturated carbon polymers. However, the mechanism of polymerization, even for benzene, the simplest aromatic hydrocarbon, is still not understood.

Polymerization of Acetonitrile via a Hydrogen Transfer Reaction from CH3 to CN under Extreme Conditions.

Acetonitrile (CH3 CN) is the simplest and one of the most stable nitriles. Reactions usually occur on the C≡N triple bond, while the C-H bond is very inert and can only be activated by a very strong base or a metal catalyst. It is demonstrated that C-H bonds can be activated by the cyano group under high pressure, but at room temperature.

Flexible sample environment for high resolution neutron imaging at high temperatures in controlled atmosphere.

High material penetration by neutrons allows for experiments using sophisticated sample environments providing complex conditions. Thus, neutron imaging holds potential for performing in situ nondestructive measurements on large samples or even full technological systems, which are not possible with any other technique. This paper presents a new sample environment for in situ high resolution neutron imaging experiments at temperatures from room temperature up to 1100 °C and/or using controllable flow of reactive atmospheres.